Microsoft has angered some of its customers after sending an automatic update to users who had previously disabled the feature.

The patch in question was an update for the Windows Updater application itself. The software checks for the latest patches from Microsoft and automatically installs them if the user so chooses.

Another option for Windows Update is to require that all updates are approved by the user prior to installation.

This feature is often enabled by users concerned about privacy or who want to ensure that the updates will not conflict with other programs.

However, news website Windows Secrets found that Microsoft Update had performed an automatic download and update in late August on the site's machines without any user notification or approval.

Nate Clinton, Windows Update programme manager, confirmed the reports and explained the reasoning behind the updates in an article on a company blog.

Clinton said that when users configure Windows Updater to ask permission before either downloading or installing updates, the application will continue automatically to update itself.

Only by configuring the application never to check for updates can users prevent the automatic installations.

"Any user who chooses to use Windows Update either expected updates to be installed or to at least be notified that updates were available," Clinton reasoned.

"Had we failed to update the service automatically, users would not have been able to successfully check for updates and, in turn, would not have had updates installed automatically or received expected notifications."

Some users, however, were not so quick to accept Clinton's justification of the process.

"Automatically installing Windows Updates patches violates our trust," said a user under the screen name 'Thingy'.

"I can guarantee that anyone who specifically chose to disable automatic installations would rather have to choose to install the new Windows Update patch, even if it meant missing out on further notifications until that was done."

A user posting under the name 'TheDave' suggested that legal action might be in order.

"There is absolutely no excuse for updating executable code on a customer's machine when the customer has selected a choice of 'let me choose whether to install them'. Period," he wrote.